1. Field of the Invention
This invention is directed generally to control systems and more specifically to programmable control systems for use with cooking systems such as deep fat fryers. Moreover, an embodiment of the invention is further directed to a programmable control system capable of storing cooking information for a plurality of food products to enable an operator to easily and consistently control the cooking operation of a deep fat fryer.
2. Description of the Prior Art
Typically, prior art deep fat fryers have a temperature probe, a heating element, which may be gas or electric for example, a temperature selector for enabling a user to select a desired cooking temperature for a particular food product and control means for controlling the heating element to be operated in different modes corresponding to the different stages of operation of a deep fat fryer. For example, there is often provided a melt mode wherein solid shortening or liquid shortening below a predetermined temperature is heated at a slow rate typically by pulsing the heating element until the liquid shortening is heated to a predetermined melt reference temperature. Typically, the heater would then be operated in a second mode wherein the temperature of the shortening is rapidly increased to a selected temperature at which cooking is to occur. While rapid increase of temperature to the selected temperature is desirable to minimize recovery time, if the temperature is raised too rapidly and/or turned off right at the selected temperature, the internal heat capacity stored in the system may cause the temperature to exceed the selected temperature. This undesirable phenomenon is known as overshoot.
In order to prevent overshoot, some prior art systems establish a temperature range, extending a predetemined number of degrees below the selected temperature, and operate the heating element in a full on mode up to this temperature range and then operate the heating element in a reduced power or pulsed mode once the temperature is within the established temperature range so that the rate of temperature increase is more precisely regulated and overshoot of the selected temperature is minimized. The effectiveness of providing this temperature range is dependent upon the temperature at which this pulse mode initiates since a tradeoff occurs between how rapidly the selected temperature can be reached and how effectively overshoot is minimized.
One major drawback with such an operating scheme is that typically the temperature range is fixed and generally can not be altered by the user. Under certain operating conditions, a user may desire faster recovery time and is willing to tolerate some chance of overshoot. Other times it may be desirable to forego the pulsed mode entirely and effectively provide thermostatic (on/off) control by setting the temperature range to zero. In other circumstances, the recovery time is less important than assuring that overshoot is minimized and a wider temperature range is preferable.
It would therefore be desirable to provide a temperature controller capable of being operated in a full on mode up to a first temperature and capable of being selectively operable in a pulse mode thereafter to bring the temperature up to the selected temperature wherein this first temperature is user selectable to provide more flexibility and enable a variety of user conditions to be taken into account to maximize product quality and consistency. For example, by selecting a first temperature near the selected temperature, faster recovery time can be obtained, that is the set point temperature can be reached in a shorter period of time since the heating element remains in a full on mode for a longer period of time. Conversely, if one wishes to minimize the chance of overshooting the set point temperature, the first temperature can be selected by the user to be substantially lower than the selected temperature thereby greater regulation of the shortening temperature can be obtained since the full on mode of the heating element is terminate well below the selected temperature. It would also be desirable to be able to effectively override the pulsed mode by providing a thermostatic on/off control so that no pulse mode occurs thereby providing faster recovery time but maximum potential for overshoot.
In some prior art systems that employ a pulsed mode as described above, this mode is typically entered directly and immediately after the full on mode. This is a drawback since, depending on operating conditions and system parameters, the pulsed mode might not be needed or desired. For example, if the temperature of the shortening is close enough to the selected temperature when the full on mode is terminated, then the internal heat capacity of the system may be capable of raising the temperature to the selected temperature. This results from the temperature rise due to the stored internal heat capacity of the system after the heating element is turned off. This thermal lag time can cause the temperature of the shortening to drift up to the set point temperature without the further application of heat such as by pulsing the heating element. Other systems do not provide any pulsed mode but rather calculate a temperature at which the heating element may be turned off such that when the heating element is turned off, the internal heat of the system will cause the cooking medium to drift up to the selected temperature. Due to various factors, precise control of the temperature of the cooking medium is not maintained.
It would therefore be desirable to cause a system to enter a wait mode between the termination of a full on mode and the initiation of the pulsed mode until a predetermined condition is met before any further control of the heating element is performed. This predetermined condition may be that the temperature rate of change is less than or equal to a predetermined value.
Some prior art systems operate such that once the selected temperature has been reached, the heating element is controlled to be periodically pulsed to maintain the temperature of the shortening at the selected temperature. Typically, these pulses have a fixed duty cycle. This is a drawback since different systems and operating conditions may require more or less pulses and frequent control of the heating element may be required to maintain the set temperature if frequent overshoot or undershoot occurs. It would be economical and efficient to minimize the number of times the heating element is pulsed and to minimize the extent to which and the number of times the selected temperature is exceeded by varying the duty cycle based on the past performance of the system.
To overcome this drawback, it would be desirable to provide correction pulses which effectively temporarily vary the duty cycle of the pulses to maintain at the selected temperature, avoid overcontrol of the heating element, avoid overshoot or undershoot and thereby provide efficient and economical operation of the heating element while maintaining the temperature at the selected temperature. Preferably, these adjustments would be based on the past history of the heat control operation for that system while operating in a maintain mode at a selected temperature for a selected product. For example, the duty cycle may be adjusted by a fixed or variable amount each time pulsing causes the temperature to exceed the selected temperature or fails to bring the temperature up to the selected temperature.
Another important consideration when using a deep fat fryer for cooking is the proper maintenance of the cooking medium. Specifically, if shortening is used, it is necessary to filter the shortening periodically to maintain cooking quality due to absorption of oils and odor from the cooked food products, and degradation of the shortening caused by breakdown thereof due to heat, extended use and other factors. The number of times a type of food product may be cooked in the same shortening before filtering is required varies from one food product to the next. For example, cooking french fries does not require the shortening to be filtered as often as is required with a breaded product, such as breaded fish. It has been found that cooking breaded fish in a deep fat fryer requires the shortening to be filtered more frequently due to various factors including the oil within the fish and the type of breading used. Other products, such as chicken require a filtration rate somewhere between french fries and fish.
Some prior art systems provide an indication that it is time to filter the shortening based on a count of the nuber of cook cycles, regardless of the type of food product being cooked. This may lead to filtration that is either too frequent or too infrequent based on the types of food cooked. It would therefore be desirable to provide an efficient and simple way to keep track of the number of times that different types of food products have been cooked and to provide an indication to the user when it is time to filter the cooking medium and thereby avoid under or over filtration of the cooking medium and further maintain the quality of the cooked product.
Another concern related to deep fat fryer cooking operations is how to deal with the situation that arises when a temporary power down condition causes an interruption of a cook cycle. One answer would be to just throw away any food that was in the process of being cooked when power down occurs. Obviously this is not a desirable alternative since it is a waste of food which is not socially or economically desirable. It would therefore be desirable to be able to continue a cook cycle that was interrupted due to a temporary power down condition if the quality of the food product can be maintained.
Another feature found in some prior art deep fat fryer systems is a load anticipation feature. Typically, the introduction of a food product into a cooking medium causes a temperature drop of the cooking medium. This phenomenon is sometimes referred to as "thermal shock." Usually, this termperature drop is not detected by the system immediately so that there is a time delay between the temperature drop due to thermal shock and the time the system recognizes and responds to the need for heat. Some prior art systems overcome this delay by turning on a heating element before the need for heat is realized by the system thereby "anticipating" the need for heat. It would however be desirable to allow a user the flexibility of selecting whether or not to use this load anticipation feature with each type of food product by programming load anticipation information into each cycle. Moreover, it would be a desirable safety feature to limit the temperature which the shortening can reach while using the load anticipation feature.
Some prior art systems cause the heating element to be controlled in an idle mode when a certain period of inactivity exists. This mode causes the cooking medium to be maintained at a temperature significantly below the selected temperature to avoid unnecessary breakdown of the cooking medium while assuring that a medium such as shortening remains in a liquid state and at a temperature that will enable satisfactory recovery time if the medium needs to be heated to the selected temperature for cooking. However, it would be desirable to provide a user with the options of selecting when and how the idle mode should be entered.
It would further be desirable to enable a computer controlled fryer to be able to store usage information so that a user may be provided with an indication of the number of times a particular cycle has been selected and the total number of times that all of the cycles have been selected.